Up-regulation of interleukin 4 receptor expression on immature (Lyt-2-/L3T4-) thymocytes.

In this report, the effect of interleukin 4 (IL-4) on the growth and differentiation of Lyt-2-/L3T4-(2-4-) thymocytes was investigated. It was found that these thymocytes proliferated extensively when cultured in the presence of IL-4 + phorbol myristate acetate without apparent differentiation to Lyt-2+ or L3T4+ cells. We also demonstrated that 2-4- thymocytes constitutively express a high affinity (dissociation constant of 20 to 40 pM) receptor for IL-4. Freshly isolated 2-4- thymocytes expressed on average about 100 IL-4 receptors per cell, but the number of receptors increased approximately 8-fold within 3 days after activation by IL-4 + phorbol myristate acetate. These findings suggest that IL-4 may play an important role in T cell ontogeny by promoting self-renewal of stem cells within the thymus.